1. Field of the Invention
This invention is in the field of rigid foams and the method for production of such foams. More particularly it relates to spray foams and pour-in-place foams and the methods for preparing such foams.
2. Description of the Prior Art
Rigid foams have been employed for a variety of uses including, for example, insulating the roofs of buildings, as insulation for solid or liquid containing tanks, doors, water heaters, and picnic coolers.
Several fully halogenated hydrocarbons (chlorofluorocarbons, commonly referred to as CFC's) normally used as blowing agents for the preparation of rigid foams are believed to cause environmental problems. For instance, CFC-11 (trichlorofluoromethane) and CFC-12 (dichlorodifluoromethane) have been implicated in the deterioration of the stratospheric ozone layer. Thus, there has been much effort in research for developing alternative blowing agents that may (partly or wholly) replace the halogenated hydrocarbons as blowing agent in the standard foam formulations. The result is the use of a variety of non-chlorofluorocarbons (non-CFCs) as blowing agents.
When rigid foams have been prepared by reacting polyisocyanates with mixtures of polyols containing non-CFCs in the presence of trimerization catalysts such as potassium octanoate, the results in many instances have not produced rigid foams with properties as good as those blown with CFC's.
Among the problems associated with these reactions is an excessive amount of heat generated during the reaction of the polyol mixture with the polyisocyanate leading to relatively high pressures in the foam as the polymerization occurs. The high pressures are undesirable since they cause spray foam to "creep" as it cures. The high pressures also lead to the presence of "pinholes" in the exterior surface of the cured spray foam. Cured spray foams having pinholes cannot be treated with a coating.
In conventional pour-in-place rigid foams, the high pressure produced by the heat of the foam reaction after cure can create deformation of or within a molded part. Accordingly, there is a need for non-CFC blown foams that do not produce excessive pressures which result in creep and/or distortion of the foam.